The present invention relates to an alignment device which can position an object to be positioned at a high accuracy within a target accuracy, and specifically to a device suitable for alignment in an apparatus such as a mounting apparatus or an exposure apparatus for wafers, etc.
For example, in a mounting apparatus for bonding wafers to each other, an aligner for positioning a wafer at a predetermined position in order to processing the wafer or mounting a chip or other parts on the wafer, or an exposure apparatus for performing a predetermined exposure on a wafer, it is necessary to position the wafer at a predetermined position with a high accuracy. As a conventional alignment device used for such positioning of an object to be positioned, for example, used is a device wherein tables adjustable in position in X-axis and Y-axis directions (a horizontal direction) and xcex8 direction (a rotational direction) are stacked and as needed a table or a head adjustable in position in Z-axis direction (a vertical direction) is combined, and in such a device, the positioning accuracy is increased by adjusting and controlling the respective positions in the respective axes directions and the rotational direction.
In such a conventional alignment device, however, because the adjustment is carried out in order with respect to the respective directions (for example, X-axis and Y-axis directions and xcex8 direction), even if a relatively high-accuracy positioning becomes possible only in one direction, there is a case where the positioning accuracy in the direction already adjusted goes wrong when the positioning in the other directions is performed, and consequently, the final positioning accuracy is limited. Further, since usually a mechanical guide is used for positioning, there is a limit in the accuracy of the guide, and also from this point of view, the final positioning accuracy is limited. More concretely, in a conventional alignment device, the possible positioning accuracy is an accuracy which cannot expect a submicron-level positioning, and therefore, a several-ten nanometer-level or several nanometer-level positioning is impossible by the conventional possible positioning accuracy.
Further, as aforementioned, since a conventional alignment device is constructed by stacking tables adjustable in position in X-axis and Y-axis directions and xcex8 direction, when an axis A except an uppermost axis is adjusted, an axis stacked above the axis A must be driven, and therefore, the efficiency of the drive and control for positioning is not good. Moreover, when the device is constructed by stacking tables adjustable in position in X-axis and Y-axis directions and xcex8 direction, the thickness (the size in the vertical direction) of the entire alignment device increases, and therefore, an apparatus incorporating this alignment device, for example, a mounting apparatus or an exposure apparatus, inevitably becomes large-sized. Further, because the distance from a guide to an uppermost positioning surface becomes large, an error of the guide is amplified, and this may give a bad influence to the positioning accuracy.
Furthermore, since the positioning in xcex8 direction is performed by adjusting a position adjusting table around a predetermined center axis, when the size of an object to be positioned, for example, a wafer, is large, particularly the alignment accuracy in the xcex8 direction deteriorates at a radially outer position in proportion to the radius of the wafer.
Accordingly, a purpose of the present invention is to provide an alignment device which is constructed not by stacking position adjusting tables for the respective directions and the rotational direction as in a conventional device, but by enabling to adjust a single movable table holding an object to be positioned in a single plane simultaneously in at least X-axis and Y-axis directions and xcex8 direction, thereby enabling to position the object to a target position at a time only by a specified one-kind position adjusting means, which can perform a high-accuracy positioning in each direction and up to a radially outer portion of the object, the efficiency of the positioning operation of which is good, and which can construct the entire apparatus to be compact.
To achieve the above-described purpose, an alignment device according to the present invention comprises a movable table for holding an object to be positioned, a plurality of movable support means for movably supporting the movable table at a plurality of positions, respectively, means for reading a recognition mark provided on the object or the movable table, and a control means for controlling the drive of the movable support means based on information from the recognition means, and positioning the object within a target accuracy by the control of the control means, wherein each movable support means comprises means having a pair of support blocks each provided to be able to contact/separate with/from the movable table and a pair of piezoelectric actuators each provided with expansible first and second piezoelectric elements extending in a substantially horizontal direction across each other and an expansible third piezoelectric element extending in a substantially vertical direction, the first, second and third piezoelectric elements being connected to a support block, and being capable of walking operation relative to the movable table by the operations that the pair of piezoelectric actuators contact/separate the pair of support blocks with/from the movable table alternately.
Namely, in the above-described alignment device, in each piezoelectric actuator of each movable support means, the support block is brought into contact with or separated from the movable table by the expansion and contraction operation (hereinafter, merely referred to as expansion operation in this specification) of the third piezoelectric element, and the support block is moved in the two-dimensional direction, that is the horizontal direction, by the expansion operations of the first and second piezoelectric elements, and accompanying with the movement, the third piezoelectric element is swung. The third piezoelectric element is repeatedly brought into contact with and separated from the movable table via the support block, accompanying therewith the swing operation is repeated, and by the condition where this operation is performed for each piezoelectric actuator of the pair of piezoelectric actuators alternately, two third piezoelectric elements operate as if they were in a walking motion relative to the movable table, and this motion is exhibited as the walking operation. This walking operation is a relative operation to the movable table, and actually, the movable table side is moved by driving the plurality of movable support means. By controlling the drive of the plurality of movable support means, the movable table can be adjusted in position in a single plane simultaneously in X-axis and Y-axis directions (horizontal direction) and xcex8 direction (rotational direction), and besides, the position of the rotational center can also be controlled arbitrarily, and therefore, the object can be moved to a target position with a high accuracy at a time by the specified movable support means using piezoelectric elements.
In this positioning, because basically it is not necessary to have a mechanical guide structure, the positioning accuracy is not limited originating from the mechanical guide structure. Further, because the movable table can be driven in a single plane simultaneously in X-axis, Y-axis and xcex8 directions by the drive of the plurality of movable support means, the distance up to the positioning surface on the movable table or on the object held on the movable table may be small from the viewpoint of this drive system due to the plurality of movable support means, and therefore, there does not occur a problem of amplification of an control error in the drive of the positioning surface ascribed to this distance, which has occurred in a case where the distance from a drive surface to a positioning surface becomes relatively large such as a case of a conventional device. Therefore, a high accuracy for positioning can be ensured. Namely, since an efficient and high-accuracy positioning can be performed at a time by the plurality of movable support means without using a mechanical guide structure, an error ascribed to the drive for positioning hardly occurs, and a high-accuracy positioning becomes possible. Further, since the drive plane in X-axis, Y-axis and xcex8 directions by the plurality of movable support means becomes substantially a single plane, the drive efficiency for positioning is good. Furthermore, because the plurality of movable support means form one set of positioning means disposed substantially on a single plane, the alignment device can be reduced in size particularly in the vertical direction, as compared with a case where position adjusting tables for the respective axes directions and the rotational direction are stacked such as a case of a conventional device.
Further, since piezoelectric elements capable of controlling the expansion amounts with a high accuracy are used for the control of the movement of the movable table by the plurality of movable support means, namely, since piezoelectric elements each having an extremely high resolution are used (at present, although the resolution of a piezoelectric element itself is less than an angstrom level, the resolution of a measurement/control system including a piezoelectric element and various equipment is about 12 nm, and it is possible to further improve the resolution to a level less than 5 nm by changing the control structure), a significantly high-accuracy positioning becomes possible. Further, even if the size of an object to be positioned becomes large, because the respective movable support means can be disposed at positions corresponding to the radially outer portions of the object, the resolution particularly in xcex8 direction can be maintained to be high.
Moreover, since the alignment device according to the present invention basically does not have a slide part, it can be installed in a vacuum chamber and the like in which it is difficult to dispose a conventional device having a slide part. Further, as described above, because the alignment device can be constructed as a type thin in the vertical direction, it becomes possible to form an opening structure at the central portion and to provide a recognition means for alignment (for example, a camera for alignment) or provide a backup member for a case accompanying pressing operation at the central-opening position or a position corresponding thereto.
Further, in the present invention, it is possible to omit the movable table and support an object to be positioned directly by the movable support means. Namely, an alignment device according to the present invention can comprises a plurality of movable support means for movably supporting an object to be positioned at a plurality of positions, respectively, means for reading a recognition mark provided on the object, and a control means for controlling the drive of the object based on information from the recognition means, and positioning the object within a target accuracy by the control of the control means, wherein each movable support means comprises means having a pair of support blocks each provided to be able to contact/separate with/from the object and a pair of piezoelectric actuators each provided with expansible first and second piezoelectric elements extending in a substantially horizontal direction across each other and an expansible third piezoelectric element extending in a substantially vertical direction, the first, second and third piezoelectric elements being connected to a support block, and being capable of walking operation relative to the object by the operations that the pair of piezoelectric actuators contact/separate the pair of support blocks with/from the object alternately.
The above-described alignment device according to the present invention may be constructed so that the coarse positioning of the object is carried out by the walking operation, and the precise positioning of the object is carried out by the expansion operations of the respective piezoelectric elements at a condition where the walking operation is stopped. Since the amount of expansion of each piezoelectric element can be controlled at a significantly high accuracy although the amount itself cannot be increased so much, it is possible to perform the positioning at a submicron level, which has been impossible in the conventional technology, and further at a nanometer level, by such a high-accuracy adjustment after the coarse adjustment due to the walking operation.
It is preferred to perform the above-described precise positioning of the object within a range of one step of the walking operation. By this, the high-accuracy fine adjustment utilizing the expansion operations themselves of the piezoelectric elements after the above-described coarse adjustment can be carried out more surely. Further, it is preferred that the swing position of the third piezoelectric element due to the expansion operations of the first and second piezoelectric elements is reset to a center position in a range of one step of the walking operation before the precise positioning of the object. By this, the high-accuracy fine adjustment utilizing the expansion operations themselves of the piezoelectric elements after the above-described coarse adjustment can be carried out in an arbitrary direction.
Further, a piezoelectric element has a property liable to be influenced by its history that the following drive amount and locus are likely to be decided by the previous drive stroke. Therefore, in order to remove an bad influence due to this property for the positioning accuracy, resetting is preferred before the precise positioning of the object so as not exhibit the influence due to the histories of the previous operations. Namely, it is preferred that the histories of the amounts of the expansion operations of the respective piezoelectric elements are reset before the precise positioning of the object.
Further, it is preferred that the properties of the expansion operations of the above-described respective piezoelectric elements are calibrated beforehand. By this, the accuracy for the control by the control means can be ensured. Although the timing of the calibration may be appropriately set, in a case where a variation of the properties of the expansion operations of the piezoelectric elements is expected, it is preferred to carry out the calibration regularly although a high frequency for the calibration is not necessary, and in that case, the calibration value is preferably renewed to the newest one.
Such an alignment device according to the present invention is suitable particularly for an apparatus requiring a high-accuracy positioning. For example, the alignment device is incorporated into a mounting apparatus for bonding wafers to each other, a wafer and a chip, or chips to each other, and the device can be used for positioning of an object to be bonded in the mounting apparatus. Further, the alignment device can be used as an aligner for positioning a wafer, etc. in order to mount a chip and other parts thereonto. Furthermore, the alignment device can be used for positioning of an object to be exposed in an exposure apparatus in order to give a predetermined exposure to a wafer, etc.